1. Technical Field
The present invention relates to a multiple segment lobe pump with reduced or zero pulsations in the outflow.
2. Related Background Art
The first lobe (air) pump was invented in 1854 by a couple of wood mill owners in Connersville, Ind. named Francis and Philander Roots and became known as ‘The Roots Blower’. The design featured two side-by-side rotors that were each shaped sort of like a two dimensional hour glass. As the rotors turned, each delivered a ‘puff’ of air, twice per revolution. The blower was intended to produce the intermittent volume of air flow for uses in their mill. In the early 1900's, engineers at the Howard Pump Company in Eastbourne, England realized that if the blower were to run at a relatively low speed, it could forcibly transport a volume of incompressible media, such as liquids or semi-solids, between two locations. With that discovery, the first lobe (transfer) pump was born.
Up until the early nineteen-seventies, the pumping mechanism of the lobe pump consisted of two parallel shafts, each fitted with a single rotor that had multiple lobes with a profile that was parallel to the axis of rotation of the respective shaft. In other words, the lobes were straight sided. Depending on the application, the number of mating lobes was usually two or three and in some cases four. However, such pumps produce flow pulsations that are undesirable in many applications and as a result, have limited their wide spread use. By its design a lobe pump is a positive displacement pump. It is capable of pumping a wide variety of liquids, gels and granular materials. Current lobe pump applications include the transport of polymers, paper coatings, surfactants, paints, adhesives and a large variety of food applications such as; berries, fruits, chopped vegetables, cereals, grains and many other food products.
Starting in the mid-1970's with the advances in machining methods, the helical lobe pump was developed. The curved nesting lobe design significantly reduced the magnitude of the pulses but did not eliminate the non-continuous pump flow characteristic. In recent years, several manufacturers realized that a continuous flow, pulsation free helical lobe is possible by increasing the ‘pumping chamber isolation region’ so as to include the extent of the helical wrap of each lobe.
Currently, four and five helical lobe, non-pulsating pumps are available from several manufacturers. In order for these pumps to be pulsation free, the housing design must provide a ‘pump chamber isolation region’ (PCIR) that spans the separation angle between the lobes plus the helical wrap angle. In the case of a four lobe design, the angular lobe separation angle is 90° and the helical wrap angle must be 90° requiring a PCIR of 180°. The distance between the two sealing arcs is, by physical geometry equal to the center distance between the two shafts. The inlet and discharge flow area is therefore equal to the rotor height times the distance between the two shaft centers.
A three helical lobe, non-pulsating pump is currently not manufactured because of the geometric limitations related to the PCIR. A three lobe design has a lobe separation angle of 120°. Adding the wrap angle required to seal a volume of flow within the pumping cavity and provide continuous pulse free flow, requires a PCIR of 240° resulting in an unworkably small inlet and discharge opening.
There is a need for designs of straight lobe pumps with reduced pulsation in the outflow. There is a need for helical lobe pumps that provide wider inlet and outlets on the pump housing. There is a need for a design that enables two and three lobe helical lobe pumps. There is a need for lobe pump designs that allow flexibility in choosing the size of the pumping chamber and the inlet and outlet dimensions of the pump. There is a need for a pump that retains all of the desirable features of a single segment lobe pump, which include the ability to handle viscous fluids, mixed media (liquid and solid) and semi-solids while providing continuous, low pulsation or pulsation-free flow.